Externalize configuration property section configuration #23972
Description
The configuration of the configuration property sections in the appendix is currently hardcoded in the DocumentConfigurationProperties task in buildSrc. When a change is made to the sections, this triggers an entire rebuild due to how Gradle treats buildSrc. It would be better if the configuration was in the spring-boot-docs module's build.gradle script. It can be declarative so it's well-suited to going there rather than being done in code.